This invention relates to chemical vapor deposition methods for providing a Bi oxide-containing film on a surface of a substrate by decomposing a precursor of Bi oxide.
Interest in ferroelectrics has increased in recent years, due to the utility of these materials in applications such as non-volatile memories. Information in these memories is stored by the polarization of a thin ferroelectric film which is placed between the two plates of a capacitor. The capacitor is connected to a transistor to form a storage cell, which controls the access of read-out electronics to the capacitor.
The information stored in the cell can be changed by applying an electric field to the thin ferroelectric film and flipping the polarization. Ferroelectric random access memories (FERAMs), unlike DRAMs (dynamic random access memories), retain the stored information if the power supply is turned off. In addition, they do not require refresh cycles. Desirable electrical properties for ferroelectrics used in memory applications include: (a) a low coercive field, which makes the use of as low a voltage supply as possible; (b) a high remanent polarization, which is needed for high reliability of information storage; (c) minimal fatigue, which is required for a long life-time; and (d) no imprint, as an imprint would alter the stored information.
Strontium bismuth tantalate (SrBi.sub.2 Ta.sub.2 O.sub.9) (SBT) is a ferroelectric material that meets all of these requirements. Significant efforts are therefore being made to integrate this material into memory devices. Capacitors in which SBT is incorporated using a sol-gel method have good electrical properties. The sol-gel method provides only a low integration density of SBT, however. To achieve a higher integration density of SBT, an alternative method, such as chemical vapor deposition (CVD), must be used.